This invention relates to an improved engine control system and method and more particularly to an improved start up control system and method for engines.
A wide variety of engine controls have been employed for internal combustion engines. These controls are frequently employed in conjunction with fuel injection systems. This is desirable because such controls and the associated fuel injection systems offer the possibility of improving engine performance while at the same time permitting efficient exhaust emission control and better fuel economy.
In many of these engine control systems and methods there is provided a separate fuel injector for each combustion chamber or cylinder of the engine. Of course, such systems offer the possibility of even more accurate control. However, these systems also somewhat add to the cost of the overall engine. Furthermore, they require a more complicated control strategy.
The engine control is particularly critical during initial start-up phase, particularly if the engine temperature at start up is below the normal engine operating temperature. During start up it is frequently desirable to provide additional fuel to compensate for starting conditions particularly for the lack of fuel in the induction tract and also the possible low temperature of the induction tract.
It is, therefore, a principal object of this invention to provide an improved engine start-up control apparatus and method for an engine.
It is a still further object of this invention to provide an improved control system and method for utilization in the starting of fuel injected engines and particularly those having multiple cylinders.
In connection with engines and, in particularly two-cycle engines, it has been proposed to employ a system whereby the idle and off-idle speed of the engine is controlled, not by the throttle valve position, but by controlling the number of operating cylinders. That is, with this type of control, the throttle valve is left in a partially-open position at speeds and loads below a predetermined amount. The engine speed and output is controlled by selectively disabling a certain number of cylinders to maintain idle speed.
As the speed is to be increased, then the number of cylinders that are operative is increased. Said another way, the disabling of the number of cylinders is diminished up until a point when further demand from the operator is accommodated by opening the throttle valve further. In addition, the number of cylinders which are operating may also be increased during this phase. This type of control system is disclosed in U.S. Pat. No. 5,579,736 issued Dec. 3, 1996 in the name of Kazuhiro Nakamura and Kimihiro Nonaka entitled "Combustion Control System For Internal Combustion Engine," the disclosure of which is incorporated herein by reference.
With such an arrangement, however, it is desirable to operate all of the cylinders during start-up. Hence, during start-up, all cylinders are operated, but after a time period then the speed of the engine is controlled by disabling some cylinders. This, obviously, gives rise to transitional problems between starting and normal engine running at low and medium speeds when the speed is controlled by disabling one or more cylinders.
It is, therefore, a still further object of this invention to provide an improved control system and method for utilization in the starting of engines and, particularly those having multiple cylinders, where the normal low speed running is controlled by disabling cylinders, but starting is accomplished by operating all cylinders.
One of the methods and systems which have been proposed for use in engine management to improve engine performance, fuel economy and exhaust emission control employs feedback control. One form of feedback control system employs an air/fuel ratio sensor such as an oxygen (O.sub.2) sensor. The oxygen sensor is positioned to receive the exhaust gases from the combustion chamber and measure the amount of oxygen in them. From determining the amount of oxygen in the exhaust gases the actual air/fuel ratio burnt in the cylinder can be determined.
Although oxygen sensor feedback control systems can offer the prospect of very efficient and effective engine control, they are quite costly. In addition, there are some engine conditions wherein the feedback control from a sensor such as an oxygen sensor are not possible. For example, under initial start up and until the oxygen sensor reaches its operating temperature, it cannot be utilized as a control system. Thus, it is generally the practice to provide an increased amount of fuel flow under this condition until the engine and the oxygen sensor reach their normal operating condition. This amount of fuel may be varied, depending upon ambient engine or atmospheric conditions.
However, if this additional amount of fuel is supplied for start-up and initial warm-up operation, the transition from this type of control to normal control can present some problems. This is particularly true when engine speed or output are controlled by cylinder disabling, as aforenoted. For example, if the transition is too severe, for example, if the mixture is leaned too suddenly, then the engine may stall. This is particularly true if the transition is made at a time before the engine reaches its normal operating temperature. In many instances, the transition is made at this time so as to improve fuel economy and exhaust emission control.
On the other hand, if the enriched mixture is maintained for a long enough time period that the engine will be assured to be at or higher than its operating temperature, then excess fuel is supplied, and again, emission control and fuel economy will suffer.
It is, therefore, a further object of this invention to provide an improved control system for an engine wherein the control system is simple and also provides effective control upon initial engine starting, particularly when low speed and load are controlled by cylinder disabling.
It is another object of this invention to provide an improved control system and method for an engine wherein the control system and method provides effective transitional control upon initial engine starting, particularly when low speed and load are controlled by cylinder disabling.